1. Field of the Invention
The present invention relates to a hand-operated chain block, and more particularly to a hand-operated chain block which is lightweight and simple in construction with respect to the hand chain wheel portion, and which permits safe and smooth hand chain operation.
2. Description of the Prior Art
Conventionally, in the structure of the hand chain wheel portion of a hand-operated chain block, safety measures for operation of the hand chain are provided, and various lightweight and simplified structures for reducing the weight of the entire chain block have been proposed.
The present inventors have proposed structures as disclosed, for example, in Japanese Utility Model Publications No. 48-19725 and No. 49-36204.
In the chain block disclosed in the Japanese Utility Model Publication No. 48-19725, a positioning dowel is formed in the hand chain guide plate, a small hole is formed in the hand chain wheel cover, and the hand chain guide plate is designed to be fixed on the chain block by engagement of a stay for hand chain wheel cover mounting and engagement of the dowel and with the small hole. The guide portion of the hand chain guide plate projects so as to cover an upper edge portion of a side window of the hand chain wheel cover.
On the other hand, the chain block disclosed in the Japanese Utility Model Publication No. 49-36204 has the hand chain cover having a split-type construction, consisting of an upper cover having a hook section so as to cover the front upward outer portion of the hand chain wheel, and a U-shaped lower cover that covers the front outer part of the hand chain wheel not covered by the upper cover. The lower cover is made of a thicker plate material than the upper cover, and guide plates for the hand chain are integrally disposed at both right and left ends. The right and left ends of the front plate of the upper cover and the upper right and left ends of the lower cover are combined, and this combined portion is fixed to the side plate of the chain block by a common bolt, while the intermediate portion of the lower cover is affixed to the side plate by another bolt.
Such structures are, however, not completely satisfactory, having the problems discussed below. Further improvements have been requested.
In the disclosure of the Japanese Utility Model Publication No. 48-19725, the structure for mounting the hand chain wheel guide plate itself is relatively simple, but, at the time of mounting, engagement of the positioning dowel and small hole is difficult, and the assembling efficiency is very poor.
Also since the guide portion of the hand chain guide plate is located in the upper edge of the hand chain wheel cover, the entire side portion of the hand chain wheel is open, and the hand chain is exposed to the outside. Accordingly, there was possibility of touching the hand chain wheel portion by hand or catching of a falling object through this open portion, which is not desirable for safety reasons.
In the structure disclosed in Japanese Utility Model Publication No. 49-36204, the guide plate for guiding the hand chain is a small piece disposed at right and left end portions of the lower cover such that nearly the entire side portion of the hand chain wheel is open, which poses safety problems.
Also, the lower hand chain wheel cover is relatively thick, and further reduction of weight is desired, but when made thin, the strength may be lowered.
In both cases, furthermore, when the hand chain is pulled and operated at a relatively high speed, for example, in the case of operation when no load is suspended on the load chain, twist (entangling) of the hand chain may not be completely cleared to the original state by the hand chain guide plate. Accordingly, the hand chain is taken up on the hand chain wheel in a twisted state, and smooth hand chain operation is impeded.